118 MOLLUSCA FROM THE CRAG. 



Fi-. 7 b is a young or perhaps broken specimen ; the straight part of the tube in 

 fig. 7 a is nearly cylindrical. 



If Serpula incrassata of Walker be the young of Cacum glabrum, it is probable the 

 shell from the Crag may be the young state of Cacum mammillatum. 



LITTORINA,* Fermsac, 1821. 

 TURBO (spec.) Linn. 

 TRICOLIA (spec.) Risso. 

 NEKJTOIDES. Brown, 1827. 

 LITOBTNA. Loven, 1846. 

 MELARAPHA. Megerle, 1832 (fide Gray). 



Gen. Char. Shell turbinate, thick, solid, and strong, ovate or globular; spire 

 acuminated, consisting of few volutions; externally smooth or striated; aperture 

 elliptical or subcircular ; peritreme entire, sharp- edged ; columella rather flattened ; 

 operculum corneous and spiral, with lateral nucleus. 



Shells of this genus have a strong resemblance in form to those of Turbo, with 

 which they have been generally placed. A considerable difference exists in the animal 

 inhabitants, and in the recent state they may be distinguished by the operculum, which 

 in this genus is thin and corneous, while in Turbo it is calcareous, thick, and ponderous; 

 in which genus, also, the shells are of a nacreous texture. They may be distinguished 

 from Phasianella, which they somewhat resemble, by the want of a polished and glossy 

 exterior. 



These animals, as the name implies, are frequenters of shallow water, near the 

 shore, and are generally found in salt water. 



As a genus, it has an extensive geographical range, being found in all latitudes ; 

 and a species is given by Mr. J. Sowerby as belonging to the Silurian system. 



1. LITTORINA LITTOREA. Linn. Tab. X, fig. 14, a k. 



TURBO LITTOREUS. Linn. Syst. Nat. 12th edit. p. 1232, 1766. 



Brown. lUust. Brit. Conch, pi. 46, fig. 1-9, 1827. 

 J. Sow. Min. Conch, t. 71, fig. 1, 1814. 



RUDIS. t. 71, fig. 2. 



LTTTOREUS. Smith. Strata Identif. p. 5, pi. 2, fig. 3, 1816. 



CARINATUS. Woodward. Geol. of Norf. t. 3, fig. 11, 1833. 



VENTRICOSUS. ... - fig. 12. 



BICARINATUS. - - fig. 13. 



SULCATUS. - fig. 14-15. 



ELONGATUS. - fig. 16-18. 



DELPHINULA CARINATA. - - fig. 9. 



LITTORINA VTJLGARIS. G. Sowerby. Gen. of Shells, fig. 1. 



SOCALIDA. Brod. and Sow. Zool. Journ. vol. iv, p. 370, 1829. 



Gray, Zool. of Beechey's Voy. pi. 24, fig. 12. 

 LITTOREA. S. Wood. Catalogue 1842. 



Nyst. Coq. foss. de Belg. p. 387, 1844. 



L. Testa variadili, ovatd, imperforata, lineis fuscis cinctd ; apice acuto ; anfractibus 



* Etym. Littus-oris, the shore. 



